(1) Field of the Invention
The present invention relates to an apparatus and a method for the formation of a wiring pattern on a substrate. More particularly, the invention relates to an apparatus and a method which can transfer the wiring material fed on a transfer plate to a substrate.
The present invention also relates to electronic devices, such as wiring substrates and wiring pattern-transferring sheets, to be used in thin display units, mechanism parts, etc. as well as to production methods therefore. Particularly, the invention is aimed at forming electrically conductive, fine wiring patterns at extremely high accuracy.
(2) Related Art Statement
(2-1) First Related Art Statement
As a technique for forming a pattern such as a wiring or a color filter on a substrate, a pattern-forming technique using photolithography is known. This pattern-forming technique is a technique used mainly in forming fine patterns, and is particularly an indispensable technique for forming semiconductor circuits. The pattern-forming technique using the photolithography is also used for forming wirings on substrates greater than the semiconductors (for example, for forming wirings on print substrates). For example, when a pattern is to be formed on a substrate in which a copper foil is bonded onto a resin substrate such as FR-4 (copper foil-bonded glass epoxy plate), such a pattern is formed on the copper plate by etching a surface of the substrate with use of the photolithography.
However, when the patterning technique using the photolithography is employed, a waste material or waste liquid is produced on etching or the like in forming the patterns. Thus, there is a problem that an equipment and a labor are required for disposing of the waste. As one of methods for solving the waste disposal problem, a method is known in which after a wiring pattern is formed on a transfer plate, the pattern is formed on a substrate by transferring the wiring pattern on the transfer plate onto the substrate. When the pattern is formed on the substrate, it is necessary that since the ordinary substrates have poor water-retaining property, a material satisfying both printability and transferability is used and further the method undergoes proper steps. For example, when an ink on the transfer plate is to be transferred on an object to be printed, a transferring method is used in which such an ink as increases its viscosity and becomes semi-solid or solid in response to an external field (electric field or magnetic filed) is placed on given locations on the surface of the transfer plate, and the external field is applied to the ink which has been so placed that the ink may be transferred onto the object, while the shape of the ink placed at the above transfer plate is being maintained, and then the ink is transferred onto the object, while the ink remains the semi-solid or solid state (For example, JP-A 8-187927).
However, when a man uses the above method in which the viscosity of the ink is varied by the external field, the material which changing its viscosity in the external field needs to be employed as the wiring material. When the wiring is formed with such a wiring material, it is feared that the resistance of the wiring changes depending upon an intensity of current passing the wiring. This poses a problem in designing a circuit. Further, the above problem is not limited to the formation of the wiring in the electric circuit. When an optical wiring is provided on a substrate, distributed light beams vary and light transmission decreases as to the material which changes with the magnetic field.
(2-2) Second Related Art Statement
A photo process and an etching process are generally used for producing fine wiring patterns such as wiring pattern substrates and wiring pattern transferring sheets as well as active circuits. Such processes have high production costs, and afford adverse effects upon environment due to their wastes. Further, it has been difficult to form circuits on curved surfaces or a plurality of flat surfaces.
Under the circumstances, circuits have been formed by transferring
circuit patterns onto surfaces of transferring objects without using the photo process or the etching process. For example, as described in JP-A 9-312460, a continuous circuit-transferring portion 21 is formed by printing a circuit pattern 26 on a base 22, and a circuit is formed by transferring a circuit pattern 26 on a surface of an object 34 by applying heat and/or pressure from a back face of the base 22.
Further, JP-A 11-207959 describes that a substrate is provided with a circuit pattern in which hydrophilic portions and hydrophobic portions are formed so that when the circuit pattern is formed on the substrate, a fluid material may not too widely spread before drying and the circuit pattern does not broken after drying.
In case that a circuit is formed by transferring a circuit pattern on a surface of transferring object, it is feared that the circuit pattern may undergo damages such as those upon the wiring when a base is peeled. Thus, such is not suitable for fine wiring.
Further, in case that hydrophilic portions and hydrophobic portions are formed to control the shape of an electrically conductive ink on a substrate, a separate patterning process is required for all substrates, and consequently, the product costs rises.
Since a circuit pattern is generally a bundle of continuously slender lines, the formation of the wiring needs to satisfy both continuity and shape accuracy for electrical conduction.
In case that a wiring substrate or a wiring pattern-transferring sheet having a circuit pattern is produced by forming a fine pattern on a support through printing with an electrically conductive ink, the viscosity of the electrically conductive ink must be investigated.
In order to form a fine pattern by printing, the electrically conductive ink used needs to have a low viscosity. This means that an ink jet type needs to discharge a very small amount of a liquid (impossible for piko liters or phenom liters of a high-viscous liquid. Further, in order that an ink may be held at a pattern formed on a printing plate (intaglio printing plates, a relief printing plate, a planograph plates), the ink needs to have a lower viscosity (In case that the viscosity is high, it is feared that contaminated ground or shrot cut occurs).
On the other hand, in order to maintain the shape of the fine pattern formed on the substrate with the electrically conductive ink, the ink needs to have high viscosity (low flowability). Since the pattern shape is not formed on the substrate based on uneven surface or difference in wettability, a low-viscosity ink such as water forms small drops. Therefore, the pattern shape cannot be maintained.